The invention relates to connectors for joining axial sections of so-called "inner duct". Such inner ducts are typically used to enclose 3 fiber optic cables. Three such inner ducts are typically positioned inside a conduit.
The enormous advantages of using fiber optic cables for telephone and other applications has fostered the installation of huge amounts of such fiber optic cable. This in turn has focused attention on the apparatus and methods for installing fiber optic cable. The inner duct used in such installations has a diameter of approximately one or two inches and is manufactured of medium or high density polyethylene. Some inner duct is manufactured with a smooth wall and, thus, has an appearance similar to polyvinyl chloride water pipe, which is often used for residential and commercial applications. Other inner duct is manufactured with a corrugated wall, which has successive axial sections with alternately larger and smaller diameters. The contour is, thus, not the contour of a helix. The present invention has particular application to the so-called corrugated inner duct.
It is highly desirable to join axial sections of the inner duct together in a manner which excludes moisture and other substances that would deteriorate the fiber optic cable. It is also highly desirable to join axial sections of the inner duct in a manner which has an axial tension strength at least as great as the axial tension strength of the inner duct itself. This is significant because the inner ducts must be pulled through a conduit into which they are installed in much the same manner that wires have historically been pulled through conduits.
The prior art includes various devices for joining axial sections of inner duct. These known sections have not been wholly satisfactory. For example, one known device is a metal sleeve having a central bore extending through it. Disposed in the bore are left and right hand threaded axial extremities, which engage respective axial sections of inner tube. This device is expensive to manufacture. In addition, it is difficult to install because of the necessity for rotating the sleeve. Other disadvantages include not being able to see the axial location of the inner tube inside the opaque metal sleeve to determine the length of the axial extremity which is actually engaging the sleeve. Still another problem concerns the use of metal, more particularly, metal which may (1) conduct electricity if there is a contact with external voltage source or (2) attract lightening.
A disadvantage of most known inner duct connectors is that it is necessary to splice the cables within the inner duct if the inner duct is damaged. In other words, if the inner duct is damaged it is necessary to cut the inner duct as well as the cables inside the inner duct in order to install a connector such as the metal sleeve-shaped connector described above.
Other prior art connectors or couplings have utilized external clamping members which interfere with cable pulling through conduits.
It is an object of the invention to provide a connector for inner duct which enables the user to see the physical location of the inner duct within the coupling.
It is another object of the invention to provide a connector which can be installed on broken axial sections of inner duct without the necessity for splicing of the cable inside the inner duct.
It is another object of the invention to provide apparatus which is non-metallic and, thus, will not conduct electricity which might damage the fiber optic cable.
It is another object of the invention to provide apparatus which is extremely simple to manufacture and which ideally includes two sections of a cylinder which are identical in construction.
It is another object of the invention to provide apparatus which has a smooth exterior to facilitate pulling of the fiber optic cables with the inner ducts surrounding them easily.
It is an object of the invention to provide a design which is simple and which has a minimum number of parts which are unique so that the cost of manufacturing individual parts as well as the cost of maintaining an inventory are minimized.